1. Field of the Invention
The invention relates to a vehicular driving force control apparatus of a vehicle having a powertrain formed by a drive source and a transmission, and to a vehicular driving force control method. More particularly, the invention relates to an apparatus and method which controls the driving force of a vehicle to suppress torsional vibration in the drivetrain.
2. Description of the Related Art
In a vehicle, the drivetrain often generates unpleasant vibrations during acceleration at which time there is an increase in the engine load. These unpleasant vibrations are mainly caused by torsional vibration of the drive shaft in the drivetrain, and are generated when engine torque that has increased with an increase in engine load includes a resonant frequency component of the drivetrain. This torsional vibration becomes more prominent the greater the required driving force (i.e., the target driving force).
Japanese Patent Application Publication No. JP-A-2003-41987 describes a control apparatus that reliably detects the manner of acceleration that includes this kind of resonant frequency component of the drivetrain and reduces the vibration. This control apparatus includes accelerator depression amount detecting means, engine speed detecting means, engine load change predicting means, filtering means, and torque reducing means. The accelerator depression amount detecting means detects a value related to the accelerator depression amount. The engine speed detecting means detects a value related to the engine speed. The engine load change predicting means predicts a change over time in a value related to the engine load in a predetermined period of time from an operation to increase the accelerator depression amount. This prediction is based on a value related to the accelerator depression amount and the value related to the engine speed when an operation by a driver to increase the accelerator depression amount has been detected based on the detection results from the accelerator depression amount detecting means. The filtering means extracts a resonant frequency component of the vehicle drivetrain from the change over time in the value related to the engine load that was predicted by the engine load change predicting means. The torque reducing means reduces the engine torque corresponding to the resonant frequency component at a timing that corresponds to the resonant frequency component that was extracted by the filtering means.
According to this control apparatus, the resonant frequency component of the drivetrain is extracted from the change over time in the value related to the engine load that is predicted to actually occur, and the engine torque is reduced to reduce this extracted resonant frequency component. As a result, it is possible to reliably ascertain the time of acceleration that will generate vibration in the drivetrain to include the resonant frequency component, while reliably reducing the vibration in the drivetrain caused by this resonant frequency component.
As described above, torsional vibration in the drivetrain becomes more prominent the greater the input to the powertrain (i.e., the greater the required driving force (target driving force)). Therefore, when the input to the powertrain is relatively large, it is effective to set the gain of the filter that extracts the resonant frequency component in the drivetrain relatively high and reduce the engine torque. On the other hand, when the input to the powertrain is small, a large amount of torsional vibration will essentially not occur. Therefore, if the engine torque is reduced using the same gain that is used when the input to the powertrain is relatively large, the effect of torsional vibration suppression is not as visible, and moreover, the response deteriorates significantly from the reduction in engine torque, resulting in deterioration of drivability and the like.
However, in the foregoing publication, there is no mention of these problems with the described control apparatus. That is, the control apparatus described above attempts to eliminate the resonant frequency component that causes torsional vibration in the drivetrain with a uniform gain during acceleration, regardless of the amount of input to the powertrain. As a result, it is not possible to solve the problem of response deteriorating when the target driving force is small.
Further, the foregoing control apparatus attempts to reduce the engine torque that corresponds to the resonant frequency component in order to suppress torsional vibration in the drivetrain. However, if control to suppress torsional vibration in the drivetrain is executed by reducing the engine torque while shift control is being executed (particularly with a power-on downshift), the engine torque may be insufficient. As a result, the engine speed will not increase quickly even after the shift into the inertia phase during shift control so it takes time to reach the synchronous speed after the shift. As a result, good shift control may not be able to be realized, with various problems possibly occurring such as a delay in the shift timing, an unpleasant sensation being felt during shifting, and delayed response after a shift.